It is known that in the assembly of compressor stator blades, which are adjustable around their longitudinal axis, and in the associated adjusting drive, these are individually aligned, by means of a device, with a reference slot which is arranged on the stator blade carrier. This is necessary so that all the blade airfoils of the compressor stator blade ring always have identical stagger angles in order to ensure a synchronous incident flow of the subsequent compressor rotor blades during operation. An asynchronous incident flow of the compressor rotor blades could lead to a vibration excitation of individual blade airfoils of the rotor blades. In unfavorable cases, this could have an effect on the rotor blades in a damaging way. In order to avoid this unwanted and potentially critical operating situation of the compressor, a check of the assembly quality by means of a conclusive measuring of the angular position of all the adjustable stator blades is necessary before putting the compressor into operation.
Up to now, the angular position of stator blades was measured by means of a universal angle gage and an auxiliary device. The auxiliary device, which was located upon the reference slot on the stator blade carrier, served as a stop for the one measuring arm of the angle gage. The rear side face of an adjusting lever, which is arranged on the rotatable compressor stator blade, served as a stop face for the second measuring arm of the angle gage, upon which the angular position of the stator blade could then be read. Contingent upon the constricted space conditions on the compressor, and depending upon the position of the compressor stator blade to be checked on the circumference, reading errors and inaccurately located measuring arms could result. This could especially be the case if the fitter has to work overhead. As a result of the erroneous inspection, it could be possible that correctly set stator blades were unnecessarily adjusted into an incorrect position, or incorrect positions of compressor stator blades were not recognized. This could altogether lead in part to unevenly set stagger angles, as seen over the circumference, of the blade airfoils of rotatable stator blades. A further source of error, which can lead to a slightly asymmetric setting of the compressor stator blades, are the tolerances by using the auxiliary device.